Networked communication devices

ABSTRACT

An aircraft emergency lighting system includes a plurality of light units arranged to guide passengers to and to identify exits in an emergency. The light units communicate wirelessly with a remote master control unit operable from the cockpit using a low power spread spectrum signal centered on a single frequency to avoid interference with onboard aircraft control and communication systems. The light units are arranged to receive and transmit any signal to and from the master controller whereby only some of the light units need be within range of the master controller. The light units include battery operated LEDs and cycle between an inoperable (sleep) condition and an operable (awake) condition to conserve power consumption and extend battery life.

This application is a §371 National Phase based on PCT/GB03/003006 filedJul. 10, 2003.

BACKGROUND

This invention concerns improvements in or relating to networkedcommunication devices and systems employing such networked devices. Theinvention has particular, but not exclusive application to systems inwhich a plurality of networked communication devices such astransceivers are arranged to communicate wirelessly with a mastercontroller to control operation of the devices and/or to provideinformation relating to the status of the devices. More especially, theinvention relates to systems employing spread spectrum communicationbetween networked communication devices and a master controller. Theinvention may be employed in aircraft to control operation of safetysystems in an emergency such as emergency lighting systems to assistevacuation of the aircraft, for example in the event of an accident, ordeployment of oxygen masks, for example following suddende-pressurisation of the cabin. The invention may also be employed toprovide information on the status of such systems and/or informationrelating to other systems relating to safety of the aircraft, forexample smoke detection systems.

Conventional electrically powered lighting systems provided in aircraftfor normal use are hard wired with electrical wiring connectingindividual light sources to a remote power source, typically storagebatteries. Such systems may be rendered inoperable following an accidentif the electrical wiring connections to the power source are damaged.For example, the electrical wiring connections may be broken by impactdamage to the structure of the aircraft, and/or by fire and/or by waterif the aircraft has to make an emergency landing on land or in the sea.

For this reason, it is a mandatory requirement to fit aircraft withemergency lighting systems at ceiling and floor level that are operableindependently of the normal lighting system to provide back-up in theevent of failure of the latter and to assist evacuation of the aircraft.

Traditionally, these emergency lighting systems have also beenelectrically powered with hard wiring connecting the light sources to aremote power source such as storage batteries separate from theelectrical lighting system for normal use. This adds considerably to theinstallation costs.

Furthermore, being electrically powered, these known emergency lightingsystems have been susceptible to failure at the time they are required.For example, damage to the power source (e.g. storage batteries) and/orthe electrical wiring connections may prevent operation of the emergencylighting system in exactly the same way that the overhead electricallighting systems for normal use may be rendered inoperable.

Another disadvantage of electrically powered emergency lighting systemsis the additional servicing and maintenance work that has to be carriedout to keep the system in good condition. Thus, the power source,electrical wiring, connections and light source such as bulbs have to bechecked regularly and any damaged or broken parts replaced.

We have previously proposed in European Patent No.0828657-B1 a floormounted emergency lighting system employing photoluminescent materialarranged in a track extending along one or both sides of the aisle. Thephotoluminescent material is operable to emit light automatically toidentify an escape route at low levels of illumination, for example ifthe normal overhead lighting is inoperable following a crash.

More particularly, the photoluminescent material is activated byexposure to a light source such as ambient light or the normal overheadlighting and releases light by means of the stored energy from suchactivation. In this way, the photoluminescent material isself-illuminating to identify an escape route for guiding passengers toan emergency exit at the time it is needed without any connections to aseparate power source such as storage batteries required by conventionalelectrically powered emergency lighting systems.

Furthermore, the emission of light by the photoluminescent material isunaffected by damage to the track(s) and the emergency lighting systemcontinues to operate even if the aircraft breaks up into several parts.As a result, the track(s) identify an escape route which passengers canfollow to an exit or to an opening in the body of the aircraft to escapein an emergency.

This system has been widely adopted with success by many aircraftoperators. However, to comply with current regulations, electricallypowered vertical exit identifiers (VEIs) have to be provided to identifythe exits below 48″. These require hard wiring connections to a remotepower source (storage batteries) and may therefore be inoperable if thewiring connections are damaged.

Similar problems exist with other safety systems typically provided inaircraft that rely on hard wiring connections to an electrical powersource to operate in an emergency. For example, drop-down oxygen masksprovided in the cabin to allow the passengers to breathe if the cabinsuddenly de-pressurises are electrically operable and may be renderedinoperable if the cause of the de-pressurisation also damages the hardwiring connections.

Accordingly, the problems and disadvantages of electrically powered hardwired safety systems on aircraft remain.

The present invention has been made from a consideration of theaforementioned problems and disadvantages of existing hard wiredelectrical safety systems used in aircraft.

Thus, it is a desired aim of this invention to provide furtherimprovements in safety systems employed on aircraft.

SUMMARY

In particular, it is preferred object of the present invention toprovide safety systems that enable the amount of hard wiring required toinstall such systems to be reduced or eliminated whereby reliableoperation in an emergency may be enhanced.

More especially, it is a desired object of the present invention toprovide a wireless lighting system, especially a wireless emergencylighting system for use in situations where rapid evacuation is criticalto safety of passengers such as in an aircraft, ship, train or coachfollowing an accident.

It is a preferred object of the present invention to provide a wirelessemergency lighting system that is operable independently of electricalconnections to a remote power source.

These and other objects and advantages of the invention in its variousaspects are described in more detail hereinafter.

According to a first aspect of the invention there is provided a systemfor a vehicle such as an aircraft comprising a plurality of networkedcommunication devices arranged to communicate wirelessly with a mastercontroller using spread spectrum communication to control operation ofthe devices and/or to provide information relating to the status of thedevices.

By employing spread spectrum communication there is no need for aphysical electrical connection between the devices and the mastercontroller. Furthermore, as the devices and master controllercommunicate using spread spectrum technology the likelihood of thesignal interfering with other vital vehicle systems is extremely low.Spread spectrum communication is also less susceptible to interferencefrom external sources compared to narrow band communication.

In one arrangement the spread spectrum communication is frequencyhopping, for example bluetooth. In a different arrangement, the spreadspectrum communication is direct sequencing. Preferably, the devices andmaster controller employ transceivers (combined transmitter andreceiver) that communicate using radio transmission.

The master controller may be capable of transmitting and receivingsignals to and from each device independently of the other devices, i.e.all the devices may be within the range of the master controller. Forsome applications, however, especially in aircraft where the shell ofthe aircraft body, seating within the cabin, bulkheads and otherstructures provide considerable interference to the transmission andreception of the signals, it may be desirable to arrange the devices sothat signals to and from the master controller are cascaded between thedevices.

In this way, devices outside the range of the master controller canreceive signals from and transmit signals to the master controller viaone or more devices within the range of the master controller. Suchcascading may permit the use of signals of low strength which reduce therisk of interference with other electrical systems of the aircraft thatmay cause malfunction of essential systems and lead to an increased riskof an accident. This is especially important during landing and take-offwhere any malfunction may cause the aircraft to crash.

The devices may be arranged in groups with at least one device in eachgroup acting as a hub to receive/transmit signals to and from the otherdevices in the group and the hub(s) of adjacent group(s) and/or themaster controller. In this way, the master controller communicates withthe hub of the closest group which communicates with the hub of the nextgroup and so on. As a result, signals are cascaded in both directions ina sequential manner along the aircraft to and from the master controllervia the hubs to all the devices.

More preferably, however, all the devices are arranged toreceive/transmit any signal. In this way, the master controller cancommunicate with any device within range which in turn can communicatewith any other device within range. As a result, signals are cascaded inboth directions in a random manner along the aircraft to and from themaster controller and all the devices. Such random communication betweenthe master controller and the devices reduces the risk of any signal toor from the master controller being terminated prematurely if any deviceis inoperable for any reason.

Preferably, each device is provided with its own power source, forexample a battery. The battery may be replaceable, for example a lithiumbattery. Alternatively, the battery may be rechargeable. For example, wemay provide each device with a re-chargeable battery and a photovoltaiccell to charge the battery. The re-chargeable battery and photovoltaiccell may be of any suitable type. For example we may use a nickel metalhydride or lithium re-chargeable battery and a photovoltaic cell basedon silicon (Si) or gallium arsenide (GaAs) technology. In this way,routine battery replacement is not required.

Each device may include a charging circuit to control operation of thephotovoltaic cell to charge the battery according to requirements. Forexample, the photovoltaic cell may be operable to re-charge the batteryif the charged level of the battery drops below a pre-determined limit.Re-charging may be controlled in response to the charged level of thebattery. Each device may provide a visual and/or audible warning offailure of the battery and/or the photovoltaic cell.

Advantageously, the system is adapted to conserve battery power andthereby extend the period of time between battery re-charging and/orbattery replacements. One way in which the battery life may be extendedis to arrange for the devices to cycle between an operable (awake)condition in which it can receive/transmit a signal and an inoperable(sleep) condition in which it does not receive/transmit a signal.

By arranging the listening time when the device is awake to berelatively short, for example of the order of a few milliseconds, wehave found that we can greatly increase the useful life of the batterywithout significantly affecting the response of the system.

Thus, if all the devices are cycling between the operable and inoperableconditions in a random manner, then at any given time, at least some ofthe devices will be operable while others are inoperable and any signaltransmitted by the master controller will be picked up andre-transmitted by any device within range that is operable. In this waythe signal will be cascaded in a random manner between the devicesaccording to when they become operable within range of the mastercontroller or a device that has already received and is re-transmittingthe signal.

In some embodiments we may provide two cycle modes with differentintervals between the operable and inoperable conditions. A longer cycletime may be provided in a stand-by mode of operation where the system isnot in regular use and it is not necessary for the devices to be rapidlycycling between the operable and inoperable conditions, and a shortercycle time in an armed mode of operation where the system may berequired to respond to a signal from the master controller in anemergency.

For example, we may provide a cycle time of 2.5 seconds in the armedmode and a cycle time of 10 seconds in the stand-by mode. Where thesystem is in regular use, for example on aircraft that are turned aroundand back in use within a short period of time, the devices may be leftin the armed mode and the stand-by mode only selected if the aircraft isout of service for an appreciable time between flights.

Preferably, each device is provided with a unique identification codeand the master controller can transmit a polling signal that requireseach device to transmit its unique identification code. In this way, thesystem can be checked to determine if any devices are inoperable bytransmitting the polling signal and checking if identification codes arenot received from any device(s). Depending on the system, the aircraftmay still be cleared for take-off if some of the devices are inoperableprovided a minimum number are still operable. Typically, theidentification codes are generated during initial set-up of the system.

Advantageously, each device is operable to carry out a “health” and“status” check in response to a test signal from the master controllerand transmit a signal to indicate if the device is operational. Themaster controller may generate a pass/fail signal to indicate if thesystem is operational.

The invention may be applied to various safety systems on an aircraft.For example, the networked devices may comprise light units of anemergency lighting system to guide passengers to and to identify theexits in an emergency. For example, the lights units may be located ator near ground level on one or both sides of the aircraft aisle(s)and/or on either side of the exits. Alternatively, or additionally, thelight units may be located at or near ceiling height on one or bothsides of the aircraft aisle(s).

Each light unit may comprise a light source such as a light emittingdiode (LED). LEDs are preferred for their low power consumption andreliability. In a preferred arrangement, the light source comprises anarray of LEDs, in particular white LEDs, to provide sufficientillumination with low power requirement.

Where the light unit is provided at an exit it may comprise a sign suchas a vertical exit identifier to identify the exit with the light sourcebeing operable to illuminate the sign and, preferably also, toilluminate an area adjacent to the sign. Where the light unit isprovided to guide passengers to an exit it may comprise a progressionsign such as an arrow to indicate the direction to an exit.

In this way, aircraft emergency lighting systems may be provided freefrom hard wiring connections to a remote power source (storagebatteries). As a result, operation of the lighting system in anemergency is not dependent on the integrity of wiring connections andeach light unit can operate independently of any other unit to providean indication of an escape route and/or an exit if the aircraft suffersstructural damage. For example, if the aircraft body separates as aresult of impact forces in a crash landing, the light units on eachseparate part may still be operational. Thus, the light units willnormally have been switched on when an emergency condition occurred andwill remain on if subsequent damage to the aircraft occurs.

According to a second aspect of the invention there is provided anaircraft comprising an emergency lighting system employing a pluralityof networked light units arranged to communicate wirelessly with amaster controller using spread spectrum communication to controloperation of the light units and/or to provide information relating tothe status of the light units.

The lighting system may be operable in an emergency to guide passengersto an exit. For example, the lighting means may comprise one or more ofexit identifiers, direction indicators, escape path markers or overheadlighting. The exit identifiers may comprise signs placed at the exits toidentify where the exits are. The direction indicators may comprisearrows arranged to indicate the direction to the exits. The escape pathmarkers may comprise light units positioned at or near floor level alongone or both sides of an aisle along which passengers can move to anexit.

According to a third aspect of the invention there is provided a controlsystem for an emergency lighting system comprising a master controllerincluding a transmitter for transmitting a spread spectrum signal, and aplurality of light units including a respective lighting means and arespective receiver responsive to the spread spectrum signal forcontrolling operation of the associated lighting means.

Preferably, each light unit includes a respective transmitter fortransmitting a broadcast signal from the master controller and/or fromanother light unit and the master controller includes a receiver forreceiving broadcast signals from the light units. In this way, the lightunits can talk to each other and to the master controller directly orindirectly via another light unit. In this way, the operation of thesystem is not dependent on all the light units being within range of themaster controller.

According to a fourth aspect of the invention there is provided anemergency lighting system comprising a transmitter operable to emit aspread spectrum signal and a receiver responsive to the spread spectrumsignal for controlling operation of lighting means.

Preferably, the transmitter is provided by a master controller and thelighting means comprises a plurality of light units each having areceiver and a transmitter. In this way, the broadcast spread spectrumsignal from the master controller can be cascaded between the lightunits and operation of the system is not dependent on all the lightunits being within range of the master controller.

Advantageously, the master controller also includes a receiver. In thisway, the master controller can receive spread spectrum signals broadcastfrom the light units, for example for checking the status of the lightunits.

According to a fifth aspect of the invention there is provided a methodof operating an emergency lighting system comprising providing atransmitter operable to emit a spread spectrum signal and a receiverresponsive to the spread spectrum signal for controlling operation oflighting means.

Preferably, the lighting means comprises a plurality of light units eachcapable of receiving and transmitting a spread spectrum signal and themethod further comprises cascading the broadcast spread spectrum signalfrom the transmitter between light units of the lighting means. In thisway, the operation of the system is not dependent on all the light unitsbeing within range of the master controller.

It will be understood that the invention is not restricted to lightingsystems and has wider application to other safety systems that may beemployed in aircraft and/or may be used to control/monitor other onboardequipment. For example, the system may be used to control deployment ofdrop-down oxygen masks in an emergency. Alternatively, the system may beused to monitor smoke alarms or other equipment to provide an indicationof the status of the condition of the aircraft or any essentialequipment. It will also be appreciated that the invention may haveapplication in locations other than aircraft.

According to a sixth aspect of the invention there is provided awireless control system for a plurality of units wherein each unitcommunicates with a master control unit using spread spectrumcommunication and is capable of receiving a signal and transmitting thesame signal whereby a signal initially broadcast by the master controlunit can be passed on to units outside the range of the master controlunit.

One or more units may include a light that is switched on by a firstsignal broadcast from the master control unit and is switched off by asecond signal broadcast from the master control unit or by the absenceof either signal after a pre-determined time. One or more units maycomprise an alternative function such as a smoke alarm or a drop downoxygen mask.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, benefits and advantages of the invention will beapparent from the following description of exemplary embodiments withreference to the accompanying drawings, in which:

FIG. 1 is a schematic lay-out of a lighting system according to a firstembodiment of the invention;

FIG. 2 shows a schematic of the interior of an aircraft to which thelighting system of FIG. 1 may be applied;

FIG. 3 is a block diagram illustrating component parts of a light unitof the lighting system of FIG. 1;

FIG. 4 is a schematic lay-out of the operating functions of the lightunit shown in FIG. 3.

FIG. 5 shows an exploded perspective view of a light unit of thelighting system of FIG. 1; and

FIG. 6 shows a schematic of an emergency lighting system according to asecond embodiment of the invention;

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2 of the accompanying drawings, there isdepicted schematically a lighting system 500 comprising a plurality oflight units 501 arranged at an array of locations A₁ . . . A_(z), B₁ . .. B_(z), C₁ . . . C_(z) . . . for control by a master control unit 502and an aircraft 510 in which the lighting system 500 may be employed toassist escape in an emergency. While the array of locations is shown inFIG. 1 as a rectangular array, it will be appreciated that the actualarray to be used will be governed largely by the geometry of theinstallation site and any applicable regulations.

The aircraft 510 has a cockpit 511 and a passenger cabin 512. The cabin512 has a plurality of seats 517 arranged in rows on either side of acentral main aisle 518. Branch aisles 519 lead from the main aisle 518to exits 513, 514, 515, 516. In this embodiment, there are four exits513, 514, 515, 516 from the cabin 512. Exits 513, 516 at the front andrear of the aircraft allow passengers to get on and off the aircraft 510in normal use and in an emergency. Exits 514, 515 are provided for usein an emergency only. It will be understood that the number and lay-outof the seats 517, aisles 518, 519 and exits 513, 514, 515, 516 may bealtered from that shown.

The light units 501 may be arranged at desired locations in the cabin512 and the master control unit 502 arranged in the cockpit 511 foroperation by the flight crew. For example, locations A₁ . . . A_(z), maybe at the exits 513, 514, 515, 516 where the light units 501 arevertical exit identifiers (VEI's). Locations B₁ . . . B_(z) may be onaisle seats 517′ where the light units 501 are mounted at or near floorlevel on one or both sides of the aisle 518 to provide a floor proximitylighting system to identify a route to the exits 513, 514, 515, 516 inan emergency. Locations C₁ . . . C_(z) may be on overhead luggagecompartments (not shown) where the light units 501 are mounted above theseats 517 to provide overhead lighting in an emergency. It will beunderstood, however, that the light units 501 may be arranged at otherlocations in the aircraft 510 as desired.

While a single master control unit 502 is shown, a second such unit maybe provided to allow operation of the light units 501 from more than onelocation if required. For example, a (primary) master control unit 502may be provided in the cockpit 511 with an optional (secondary) mastercontrol unit 502 located at the rear of the aircraft 510 for operationby cabin staff. Additional (secondary) master control units 502 may beprovided at other positions within the aircraft 510 if desired, forexample adjacent to exits 513, 514, 515, 516.

The additional (secondary) units may be activated automatically inresponse to activation of the main (primary) master control unit 502.Alternatively, the main (primary) and additional (secondary) controlunits may be arranged so that each unit is activated automatically inresponse to activation of any one of the units. Alternatively oradditionally, the additional (secondary) units may be activatedmanually, for example by switches.

In a modification, the (primary) master control unit 502 may be locatedin the cabin 512 at the front of the aircraft 510 and connected to aswitch (not shown) in the cockpit 511. In this way, shielding of signalstransmitted to and from the (primary) master control unit 502 by thebulkhead separating the cabin 512 from the cockpit 511 may be avoided.The master control unit 502 may include a master switch on a membranepanel to over-ride the cockpit switch.

This arrangement is suitable for both new build and retrofitinstallation of the emergency lighting system 500 in aircraft. Thus,when replacing an existing hard wired system, the (primary) mastercontrol unit 502 may be connected to an existing switch in the cockpit511 for operating the original emergency lighting system. The lightunits 501 may be installed in place of the existing emergency lights.Alternatively, the light units 501 may be modified for connection to theexisting emergency lights, for example by replacing a light sourcewithin the light units 501 with a connector for coupling to an existinglight.

In this way, a hard wired emergency lighting system can be replaced witha wireless system during a re-fit with minimum disruption to the layoutof the existing emergency lighting system. Thus, each light source ofthe existing emergency lighting system (both internal and external) maybe connected to a modified light unit 501 permitting wireless controlvia a master control unit 502.

Referring now to FIG. 3, each light unit 501 is similar and comprises amother board including radio module (transceiver) 503 for receiving andtransmitting spread spectrum signals and a code generator 504 formodulating such signals.

The code generator 504 generates a code division multiple access (CDMA)spreading sequence code with random code offsets that protect againstco-channel interference causing a failure to receive where a module 503receives two or more similar power signals carrying the same message.

The light unit 501 further comprises a battery 505, a light control 506,a contactless reader 508, a status LED 509 and a microcontroller 507 forcontrolling operation of the unit 501.

The battery 505 provides the power source for the functions of the lightunit 501. The battery 505 is detachable for removal and replacement witha new battery when required. The light control 506 controls operation ofa light source described later to provide illumination when the lightunit 501 is switched on in response to an appropriate on-signalbroadcast from the master control unit 502.

The light unit 501 may be switched-off in response to an appropriateoff-signal broadcast from the master control unit 502. Alternatively,the light unit 501 may be switched off automatically a pre-determinedtime after being switched on in the absence of an on-signal broadcastfrom the master control unit 502.

The reader 508 may employ a very short range low power radio signal andbe used to carry out programming of the microcontroller 507 and/or forfault analysis if the light unit 501 malfunctions. This may assistrepair of the unit 501 if required. The status LED 509 provides a visualindication of the health of the unit 501. For example, the LED 509 maybe illuminated to indicate the unit 501 is operational. In this way, aninspection of each unit 501 can be made to locate any faulty units 501.

Each light unit 501 is arranged to conserve battery life. For example,the unit may cycle between a state in which it is “asleep” and does notrespond to signals broadcast from the master control unit 502 and astate in which it is “awake” and capable of listening for and respondingto a signal broadcast from the master control unit. The unit 501 may bearranged to be “awake” for very short periods of time, for example a fewmilliseconds, and to be “asleep” for longer periods of time, for exampleseveral seconds.

The unit may be arranged to operate with a longer duty cycle in a“stand-by” mode in which it is awakened every 10 seconds, or with ashorter duty cycle in an “armed” mode in which it is awakened every 2.5seconds. It will be appreciated that these time periods are merelyexemplary and they may be shorter or longer as desired. Stand-by mode isappropriate when an aircraft 510 is not in use with armed mode beingselected when the aircraft 510 is ready for boarding by passengers.

For long periods of non-use such switching between stand-by and armedmodes may reduce power consumption and extend battery life. In someapplications, however, where the aircraft 510 is in regular use thestand-by mode may be omitted or simply not selected. We believe thatreductions in power consumption by avoiding regular switching betweendifferent modes, for example between stand-by and armed modes, mayexceed any savings provided by using the stand-by mode leading to animprovement in battery life. Furthermore, employing one mode onlyeliminates any differences due to use and non-use and may enable batterylife to be controlled in a more predictable, reliable mannersubstantially independent of the operational duty cycle such thatbattery replacement can be carried out at regular intervals, for exampleduring routine servicing.

The radio module 503 of each light unit 501 is arranged to receive aspread spectrum signal originally broadcast by the master control unit502, and to retransmit that signal. In this way, not all of the units501 have to be within range of the master control unit 502 as units 501that are outside the range of the master control unit 502 willeventually receive the retransmitted signal from one of the other units501. As a result, a low power signal having a limited range can be usedand transmitted in cascade manner throughout an aircraft to reach alight unit at each of the array of locations.

As will be appreciated, the light units 501 receive and re-transmit anybroadcast signal from the master control unit 502 or from another lightunit when they are awake and the time taken for all light units toreceive the signal will depend on duty cycle of the units 501. Thus, itwill take longer in the stand-by mode for the signal to reach all lightunits 501 than in the armed mode. This is not considered to cause anyproblem as the stand-by mode is only intended to be used when theaircraft 510 is not in use, for example when grounded between flights,and the armed mode will be selected when the aircraft 510 is in service.

The use of low power spread spectrum signals is beneficial in achievinglong battery life and low risk of interference with other systems in theaircraft 510. It also avoids or greatly reduces any risk of activating asimilar system installed on any nearby aircraft, for example duringmaintenance testing when the aircraft 510 is on the ground, orinterfering with any signals transmitted to and from the aircraft. Forexample, we have found that a spread spectrum signal centred on a singlefrequency above or below the 345 MHz frequency that is used as standardby landing beacons can be employed and avoids interference with otheraircraft systems. In particular, a low power signal centred on afrequency of 310 MHz or 315 MHz may be used with a power density of lessthan 1 microwatt. It will be understood, however, that a spread spectrumsignal centred on other frequencies with other power densities may beemployed as desired.

As will now be appreciated, the above described control system has highredundancy, since each light unit may be within transmission range ofseveral other units, a signal will be received and re-transmitted in arandom manner when a light unit is awake. The use of CDMA ensuresco-channel interference does not occur to cause failure of a light unitto receive the signal. In this way, the need for synchronisation of theduty cycles or timed multiple transmissions of signals that wouldcomplicate the system and increase the time required to activate all thelight units is avoided. As a result, it is not necessary for all lightunits to be awake at the same time and failure of one or a few unitswill have little overall effect on operation of the system, simply alack of illumination from the failed units.

The operating functions of the lighting systems 500 will now bedescribed in more detail with additional reference to FIG. 4. Oninstallation of the system 500, an initialisation signal may bebroadcast by the master control unit 502. This will be received byneighbouring light units 501 initially in stand-by mode, andretransmitted. When a light unit 501 receives such an initialisationsignal it will generate a unique identification signal and transmit thatas well. Eventually, such identification signal will return to themaster control unit 502 which responds by sending back anacknowledgement and a unique registration code for registration of thelight unit 501.

A polling signal may be broadcast by the master control unit 502 toallow routine checking of the light units 501 to be carried out, forexample on a daily basis, for maintenance purposes. Plainly lack ofresponse from any particular light unit 501 will indicate its failure.The time taken for these one-off or routine operations will clearlydepend on the duty cycle in stand-by mode. This is not an emergencyoperation and a balance has to be achieved between convenience and longbattery life. We have found that a suitable compromise is achieved witha wake/sleep cycle of about 10 seconds.

During flight preparation, flight crew may cause the master control unit502 to send out an arming signal to bring each light unit 501 into thearmed mode with a shorter duty cycle, or this may be arranged to occurautomatically on initiation of some other flight-preparatory operation.Again, activation into the armed mode may take some time, but this canproceed while the flight crew are attending to other duties and it isnot envisaged that any delay will be caused.

The wake/sleep cycle while in armed mode will govern the response timeof the system in an emergency situation. We have found that computersimulations predict that for tested arrangements with a wake/sleep cycleof 2.5 sec and a wake time of about 3 ms in the armed mode, at least 50%of the light units installed in an aircraft can be switched on within3.5 seconds.

Thus, for example, in a Boeing 747 with 160-190 units, about 90% of theunits are woken up and the emergency light switched on well within 4 secand the process is completed within 4.6 sec. In a Boeing 737 with 30-40units, 90% of the units are woken up and the emergency light switched onwithin 4.5 sec and the process is completed within 5.8 sec. In anEmbraer 145 with 22 units, 90% of the units are woken up and theemergency light switched on within 3.5 sec and the process is completedwithin 4.3 sec.

It is interesting to note that these response times are not dependent onthe number of light units involved in any immediately obvious way. Webelieve that these response times are quite acceptable, but they may bereduced further by reducing the period of the wake/sleep cycle in thearmed mode.

The master control unit 502 may comprise the mother board describedabove for the light units 501 with a daughter board including additionalcircuitry such as a master control unit interface, a debug interface andhard wiring to a power supply. In this embodiment, all the light units501 are provided with the same firmware so that, if any unit 501 detectsit is connected to a master control unit panel or cabin switch, it willrespond to the stimuli accordingly.

The master control unit 502 may provide an indication of the status ofeach light unit 501. For example, the position of each light unit may beindicated on a screen connected to the master control unit 502 and theposition is illuminated in response to a polling signal broadcast by themaster control unit if the light unit is operational. In this way anyfailed unit can be readily identified.

Alternatively, the master control unit 502 may provide an indication ofthe overall condition of the system. For example a signal may begenerated if the response to a polling signal is received from asufficient number of lights to render the system operational. The mastercontrol unit 502 can identify the light units responding to the pollingsignal and prevent the signal being generated if the number of failedunits detected in any area or zone exceeds a pre-determined limit.

The master control unit 502 may also control operation of a light toprovide illumination in an emergency, i.e. one of the light units 501may comprise the master control unit 502.

The system may include a capability for on-board diagnostics. Thus, themaster control unit 502 may store diagnostic (maintenance) informationand have an output connection to a detachable PDA (Personal DigitalAssistant) or a laptop or other similar suitable device to download theinformation when required. Alternatively or additionally, the mastercontrol unit 502 may input the information into an onboard aircraftcentral control unit or system that may provide an output in anysuitable form, for example a visual display. The master control unit mayeven be provided as part of the onboard central control unit or system,for example as original equipment on new build aircraft.

Referring now to FIG. 5, each light unit 501 positioned at an exit 513,514, 515, 516 comprises a housing 530 of rectangular shape containing alight source 531 that illuminates an exit sign 532 to identify the exitand also provides general illumination of the area adjacent the exit viawhite lenses 533 of polycarbonate or other suitable material on eitherside of the exit sign 532.

The exit sign 532 consists of the word “exit” in a colour contrastingwith the background so as to be visible when the light unit 501 isilluminated. The letters may be translucent and the background opaque sothat the word “exit” is illuminated on a dark background or thebackground may be translucent and the letters opaque so that the word“exit” appears dark on an illuminated background. Alternatively, theletters and background may be of translucent contrasting colours.

The sign 532 may comprise a separate, detachable insert and a set ofinterchangeable inserts provided with the word “exit” in differentlanguages by means of which the light unit 501 can be adapted to meetthe language requirements of different countries by selection andfitment of the appropriate insert.

Alternatively or additionally, inserts may be provided with other wordsor markings according to the position and use of the light unit 501. Forexample, where the light unit 501 is employed to identify an escaperoute along the aisles 518, 519, the insert may be provided with apicture such as a direction indicator (e.g. an arrow) for guidingpassengers towards an exit 513, 514, 515, 516. A combination of a wordand picture may be provided.

The inserts may clip into the housing. Alternatively, the sign 532 maybe provided as part of a removable cover allowing fitment of differentcovers for changing the sign.

The light source 531 comprises a plurality of white LEDs 534. White LEDs534 are used because of their low energy consumption and reliability.However, it will be understood that the light source 531 can be of anytype including coloured LEDS, incandescent bulbs, fluorescent bulbs orotherwise. The LEDs 534 are mounted on a back wall 535 having a whitesurface to aid the emission of light. Suitable LEDs 534 comprise whiteLEDs (ex. CREE) having the following specification:

-   -   Forward Voltage 3.6V    -   Forward Current 20 mA (Peak 100 mA)    -   Power Dissipation 120 mW.

The battery 505 is positioned on the back wall 535 locally to the LEDs534. In this embodiment, the battery 505 comprises a lithium batteryhaving the following specification:

-   -   Lithium Sulphur Dioxide G36 ‘A’ (ex.SAFT)    -   Open Circuit Voltage 3.0V    -   Max continuous current 1000 mA    -   Nominal capacity (drain) 1700 mAh (100 mA)

This provides sufficient capacity to operate the lighting system for 10minutes (minimum) up to 20 minutes to meet current emergency lightinglegislation for aircraft and allow for regular testing of the systemover a period of time to ensure the system remains fully operational.The light unit 501 could include means (not shown) to provide a visualand/or audible warning of low battery power level requiring replacementof the battery 505.

The light unit 501 may be operable to carry out a “health” and “status”check in response to a test signal from the master control unit 502 andtransmit a signal with its individual identification code or number tothe master control unit 502 to indicate if the unit is operational. Inthis way, the master control unit 502 can monitor the “health” and“status” of all the light units 501 on the aircraft to determine if thelighting system meets the minimum equipment list (MEL) requirements fortake-off (dispatch). For example, the master control unit 502 maygenerate a visual or audible signal on completion of a check to indicateif the lighting system has passed or failed, for example a green lightfor pass and a red light for fail.

It will be understood that the invention is not limited to theembodiment above-described. For example FIG. 6 shows a second embodimentof a lighting system 600 according to the invention in which a pluralityof units 601 (four only shown for convenience) are arranged at differentlocations in an aircraft, for example spaced apart along the length ofthe cabin, and are arranged to receive and re-transmit signals from themaster control unit 602 and from other units 601. In this embodiment,however, the signals are cascaded in a sequential manner between themaster control unit 602 and the first unit 601A, between the first unit601A and the second unit 601B and so on to the last unit 601D.

Each unit 601 may include a light source and the system may operate insimilar manner to switch the light sources on in response to a broadcastsignal from the master control unit 602 cascaded between the light units601. Alternatively or additionally, each unit 601 may act as a hubcontrolling a group of sub units that may be arranged as part of alighting system, for example exit identifiers, aisle escape routemarkers etc.

This arrangement relies on each hub unit 601 receiving andre-transmitting the signal in sequence along the aircraft and could beprematurely terminated if one of the hubs is inoperable for any reason.To reduce the risk of such malfunction preventing operation of thelighting system when required, one or more additional (secondary) mastercontrol units may be provided at spaced locations within the aircraft.The additional (secondary) units may be activated automatically inresponse to activation of the main (primary) master control unit 602.Alternatively, the main (primary) and additional (secondary) controlunits may be arranged so that each unit is activated automatically inresponse to activation of any one of the units. Alternatively oradditionally, the additional (secondary) units may be activatedmanually, for example by switches.

As will now be apparent from the foregoing description of exemplaryembodiments, the present invention significantly reduces the amount ofwiring required in an emergency lighting system.

In particular, wiring connections between individual light units and aremote power source are eliminated by providing each light unit with itsown local power source and arranging for the light units to be operatedby wireless transmission of a control signal using spread spectrumcommunication.

As a result, there are no wiring connections that can be broken in anaccident to render the emergency lighting inoperable and individuallight units will continue to operate even if the sections of theaircraft separate.

Furthermore, installation of the emergency lighting system in both newand existing aircraft is facilitated with potential cost savings byeliminating the wiring connections employed in conventional electricallypowered systems.

Additionally, by allowing the light units to talk to each other andcascade signals broadcast from the master control unit and from otherlight units, a wide path diversity is provided fortransmitting/receiving signals that significantly reduces or eliminatesthe chance of loss of communication. In particular, the light units maybe arranged so that line of sight is always provided whatever pathsignals are transmitted/received between the units and the mastercontrol unit.

In this way, the emergency lighting system is not dependent on theaircraft configuration allowing the aircraft to be re-configured withdifferent arrangements of seats, bulkheads, galleys, toilets, etc. As aresult, the emergency lighting system has high utility and can beadapted for different aircraft configurations in a simple and effectivemanner.

Moreover, the emergency lighting system is reliable and essentiallymaintenance free over the operating life of the battery employed topower the light units offering further potential cost savings.

These advantages are of particular benefit for installation of thelighting system in an aircraft where reliability and safety requirementsare very important. For example, an aircraft is grounded if theemergency lighting system is faulty and significant costs may beincurred for an operator if a take-off slot has to be vacated due to afault in the emergency lighting.

As will be appreciated, the use of spread spectrum communication allowsthe lighting system to be utilised in aircraft where the spread spectrumradio signal is extremely unlikely to interfere with other electronicsystems in the aircraft. This is an important characteristic feature ofthe invention as interference with other systems in the aircraft couldcause the systems to malfunction. In extreme cases this could result inthe plane crashing.

It will be appreciated that the above-described embodiments are intendedto illustrate the diverse range and application of the invention tolighting systems that can be used in an emergency and that any featuredescribed can be used separately or in combination with any otherfeature of the same or different embodiments to provide a lightingsystem having the benefits and advantages described herein.

It will also be understood that the invention is not limited to theabove-described embodiments and that modifications and alterations canbe made within the scope of the invention described herein. For example,the control signals could be transmitted using microwaves, infra-redlight or some other form of electromagnetic radiation providing wirelesscommunication.

The emergency lighting system may include light units on the outside ofthe aircraft. For example, external light units may be used toilluminate an escape chute for passengers to slide down from an exitwhen escaping the aircraft. The “health” and “status” of such externallight units may be tested in similar manner to the light units withinthe aircraft to ensure these meet the MEL requirements for take-off.

Parts of the wireless emergency lighting system above-described may becombined with other emergency lighting systems to provide a hybridsystem. For example, we may provide a hybrid system comprisingwirelessly controlled light units as described above to indicate theexits (VEI's) and photoluminescent guide means mark an escape route todirect passengers to the exits. For example we may providephotoluminescent tracks at or near floor level along one or both sidesof the aisles. The photoluminescent tracks may be of the type disclosedin our European patent No.0828657-B1 the contents of which areincorporated herein by reference.

Moreover, while the lighting system has been described with particularreference to aircraft, it will be appreciated that it could be employedin other situations where it is desired to assist evacuation in anemergency, for example in ships or trains or in buildings.

Furthermore, while the invention has particular application to emergencylighting systems in aircraft as described above, it will be understoodthat the invention is not limited to such use and that other safetyfunctions within an aircraft may be switched on and off in similarmanner using the same network. For example, signs capable ofillumination such as no smoking signs, seat belt fastening signs, andexit signs may be switched on and off using spread spectrumcommunication.

Spread spectrum communication may also be used to control and/or monitorother equipment in the aircraft. For example smoke alarms at variouslocations in the aircraft may communicate with a master control unitusing wireless spread spectrum communication to provide a warning ifsmoke is detected and identify the position of the smoke alarm that hasbeen actuated. Similarly, wireless spread spectrum communication may beused to control drop down oxygen masks and provide an indication ofdeployment. Such other equipment may be registered to provide a uniqueidentification allowing routine monitoring of the status (health) ofeach unit to be carried out in similar manner to the emergency lightingsystem previously described.

Other modifications and improvements will be apparent to those skilledin the art and are deemed within the scope of the invention.

1. A system for a vehicle, said system comprising a plurality ofnetworked communication devices arranged to communicate wirelessly witha master controller using spread spectrum communication to controloperation of said devices and/or to provide information relating to thestatus of said devices, and wherein said devices are arranged toreceive/transmit any signal so that signals to and from said mastercontroller are cascaded between said devices in a random manner andwherein each device has its own battery power source and is arranged tocycle between an operable (awake) condition in which it canreceive/transmit a signal and an inoperable (sleep) condition in whichit does not receive/transmit a signal and said devices cycle between theoperable and inoperable conditions in a random manner.
 2. The systemaccording to claim 1 wherein the cycle time is of the order of a fewseconds.
 3. The system according to claim 1 wherein each device can beswitched between two cycle modes with different intervals between theoperable and inoperable conditions.
 4. The system according to claim 3wherein stand-by and armed modes of operation are provided with saidstand-by mode having a longer cycle time than said armed mode.
 5. Thesystem according to claim 1 wherein each device has a listening time inthe awake condition of a few milliseconds.
 6. The system according toclaim 1 wherein each device is provided with a unique identificationcode and said master controller can transmit a polling signal thatrequires each device to transmit its unique identification code.
 7. Thesystem according to claim 6 wherein said identification codes aregenerated by an initialization signal during initial set-up of thesystem.
 8. The system according to claim 1 wherein each device isoperable in response to a test signal from said master controller totransmit a signal to indicate if the device is operational.
 9. Thesystem according to claim 1 wherein said master controller is operableto emit a signal centered on a single frequency.
 10. The systemaccording to claim 1 wherein said battery is replaceable, for example alithium battery.
 11. The system according to claim 1 wherein saidbattery is rechargeable.
 12. The system according to claim 11 whereineach device includes a charging circuit to control operation of aphotovoltaic cell to charge said battery if the charged level of thebattery drops below a pre-determined limit.
 13. The system according toclaim 1 wherein each device provides a visual and/or audible warning offailure of said battery.
 14. The system according to claim 1 whereinsaid networked devices comprise light units of an emergency lightingsystem.
 15. The system according to claim 1 wherein at least two mastercontrollers are provided for communicating with said networked devicesusing spread spectrum communication.
 16. The system according to claim15 wherein one of said master controllers is a primary controller andeach additional master controller is a secondary controller operableautomatically in response to activation of the primary controller. 17.In a passenger vehicle, a wireless emergency lighting system for guidingpassengers to an exit, the system comprising a master controller and aplurality of battery operated light units arranged, when illuminated, toidentify a route to said exit, each light unit being capable ofreceiving and transmitting a spread spectrum signal and being arrangedto receive and retransmit any signal so that signals to and from saidmaster controller are cascaded between said light units in a randommanner, wherein each light unit is arranged to cycle between an operable(awake) condition in which it can receive and transmit a signal and aninoperable (sleep) condition in which it does not receive and transmit asignal, wherein said light units are arranged to cycle between saidoperable and inoperable conditions in a random manner.
 18. The vehicleof claim 17 wherein said light units comprise at least one exitidentifier placed at said exit to identify where said exit is.
 19. Thesystem according to claim 17 wherein said light units comprise escapepath markers positioned at or near floor level along one or both sidesof an aisle along which passengers can move to said exit.
 20. A methodof operating an emergency lighting system comprising providing aplurality of light units each capable of receiving and transmitting aspread spectrum signal, arranging said light units to receive/transmitany signal so that signals to and from a master controller are cascadedbetween said light units in a random manner, providing each light unitwith its own battery power source, arranging each light unit to cyclebetween an operable (awake) condition in which it can receive/transmit asignal and an inoperable (sleep) condition in which it does notreceive/transmit a signal, and arranging said light units to cyclebetween said operable and inoperable conditions in a random manner.